I looked at Accumate about 14 months ago when the battery in my SL was playing up. Fine if you keep the car in a garage with mains power, not so practical otherwise. My car lives on the drive, so I'd have needed the power unit in my sitting room and a hole in the wall to run the cable out to the car - which wouldn't have been very popular! Anyway my problems were solved by fitting a new battery
As been said by others I used to use an optimate for my Ducati before I sold it. It brought my dead battery back to life. Now use the Accumate for my car and it performs 100%. I do keep the car in the garage with mains supply handy